• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.84-86
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• 2018

Active hybrid solid state transformer(AHSST) is newly emerging as a device to maintan the power quality of power distribution. AHSST has a simple structure in which a power electronics device is connected in series to a conventional distribution transformer. The connected power electronics device maintains the constant voltage regardless of the primary grid voltage fluctuation through the secondary voltage control to improve the power quality. It also has a simple structure compare to conventional solid state transformer system and can achieve the same performance with fractionally-rated converter. This paper proposes an multi-level converter based on AHSST system that has a simpler control method and wider voltage control range than the conventional AHSST. The proposed system is verified by simulations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.513-516
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• 2004

In this paper, a PWM Cuk AC-AC converter for power quality improvement of custom power is presented. The PWM Cuk AC-AC converter that is used in VVCF applications such as AC line conditioner, phase shifter is modelled by using complex circuit DQ transformation whereby the static characteristics equations such as voltage gain and power factor is analytically obtained. Finally, the PSIM simulation show the validity of the modelling and analysis.

• Journal of Power Electronics
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• v.13 no.2
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• pp.197-205
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• 2013

In energy injection resonant AC-AC converters, due to the low frequency effect of the AC input envelope and the low energy injection losses requirement, the constant and steady control of the high frequency AC output envelope is still a problem that has not been solved very well. With the aid of system modeling, this paper analyzes the mechanism of the envelope pit on the resonant AC current. The computing methods for the critical damping point, the falling time and the bottom value of the envelope pit are presented as well. Furthermore, this paper concludes the stability precondition of the system AC output. Accordingly, an optimal control method for the AC output envelope is put forward based on the envelope prediction model. This control method can predict system responses dynamically under different series of control decisions. In addition, this control method can select best series of control decisions to make the AC output envelope stable and constant. Simulation and experimental results for a contactless power transfer system verify the control method.

• Journal of Power Electronics
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• v.14 no.1
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• pp.183-193
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• 2014

Due to the requirements for high reliability and accuracy, safety issues for airbag ignition systems need to be studied. In this paper, a high-voltage piezoelectric converter is designed to improve these requirements in airbag ignition systems. The proposed converter includes an inverter drive circuit, a Rosen piezoelectric transformer (PZT), an output circuit and a feedback control circuit. The key components of the high-voltage piezoelectric transformer are analyzed in detail. In addition, the proposed converter system is simulated and implemented for testing. The experimental results show that when the power supply is turned on, the charging time is less than 800ms. Furthermore, the output voltage of this converter can be kept between 2.9kV and 3.1kV, under high-efficiency constant current charging mode and zero-voltage switching conditions.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.226-228
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• 2006

This paper presents the two lossless auxiliary inducors-assisted voltage source type half bridge(single ended push pull:SEPP) series resonant high frequency inverter for induction heated fixing roller in copy and printing machines. The simple high-frequency inverter treated here can completely achieve stable zero current soft switching (ZCS) commutation forwide its output power regulation ranges and load variations under constant high frequency pulse density modulation (PDM) scheme. Its transient and steady state operatprinciple is originally described and discussed for a constant high-frequency PDM control strategy under a stable ZCS operation commutation, together with its output effective power regulation charactertics-based on the high frequency PDM strategy. The experimenoperating performances of this voltage source SEPP ZCS-PDM series resonant high frequency inverter using IGBTs are illustrated as compared with computer simulation results and experimenones. Its power losses analysis and actual efficiency are evaluated and discussed on the basis of simulation and experimental results. The feasible effectiveness of this high frequency inverter appliimplemented here is proved from the practical point of view.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.271-275
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• 2001

In this paper, proposes a novel AC-DC converter of high power factor and high efficiency by partial resonant method. The input current waveform in proposed circuit is got to be a discontinuous sinusoidal form in proportion to magnitude of ac input voltage under the constant duty cycle switching. Thereupon, the input power factor is nearly unity and the control circuit is simple. Also the switching devices in a proposed circuit are operated with soft switching by the partial resonant method. The result is that the switching loss is very low and the efficiency of system is high. The partial resonant circuit makes use of a inductor using step up and $L^2SC$ (Loss-Less Snubber Condenser). The switching control technique of the converter is simplified for switches to drive in constant duty cycle. Some simulative results and experimental results are included to confirm the validity of the analytical results.

• Journal of Power Electronics
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• v.11 no.2
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• pp.148-155
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• 2011

Direct torque control(DTC) of induction machines is known to offer fast instantaneous torque and flux control with a simple control structure. However, this scheme has two major disadvantageous, namely, a variable inverter switching frequency and a high torque ripple. These problems occur due to the use of hysteresis comparators in conventional DTC schemes, particularly in controlling the output torque. This paper reviews the utilization of constant frequency torque controllers (CFTC) in DTC to solve these problems while retaining the simple control structure of DTC. Some extensions of the work in utilizing a CFTC will be carried out in this paper which can further reduce the torque ripple. This is particularly useful for a system which has a limited/low sampling frequency. The feasibility of a CFTC with an extended carrier frequency in minimizing the torque ripple is verified through experimental results.

• Journal of Power Electronics
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• v.14 no.2
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• pp.351-361
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• 2014

The discrete torque generation mechanism and inherently nonlinear magnetic characterization of switched reluctance motors lead to unacceptable torque ripples and limit the application of these motors. In this study, a phase current profiling technique and torque sharing function are proposed in consideration of magnetic saturation effects and by minimizing power loss in the commutation area between the adjacent phases. Constant torque trajectories are considered in incoming and outgoing phase current planes based on nonlinear T-i-theta curves obtained from experimental measurements. Optimum points on constant torque trajectories are selected by improving drive efficiency and minimizing copper loss in each rotor position. A novel analytic invertible function is introduced to express phase torque based on rotor position and its corresponding phase current. The optimization problem is solved by the proposed torque function, and optimum torque sharing functions are derived. A modification method is also introduced to enhance the torque ripple-free region based on simple logic rules. Compared with conventional torque sharing functions, the resultant reference current from the proposed method has less peak and effective values and exhibits lower copper loss. Experimental and simulation results from a four-phase 4 KW 8/6 SRM validate the effectiveness of the proposed method.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.429-430
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• 2011

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology with coupled inductors. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charging mode, constant-current mode, and constant-voltage mode. The pre-charging mode employs the staircase shaped current profile to accomplish shorter charging time while maintaining the reliable operation of the battery. The proposed system is able to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 67A. The optimal discharging algorithm for Vehicle to the Grid (V2G) operation has been adopted to maintain the discharging current of 1C. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system.

• Advances in aircraft and spacecraft science
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• v.7 no.1
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• pp.53-78
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• 2020

Automatic trajectory planning is an important task that will have to be performed by truly autonomous vehicles. The main method proposed, for unmanned airplanes to do this, consists in concatenating elementary segments of trajectories such as rectilinear, circular and helical segments. It is argued here that because these cannot be expected to all be flyable at a same constant speed, it is necessary to consider segments on which the airplane accelerates or decelerates. In order to preserve the planning advantages that result from having the speed constant, it is proposed to do all speed changes at maximum deceleration or acceleration, so that they are as brief as possible. The constraints on the load factor, the lift and the power required for the motion are derived. The equation of motion for such accelerated motions is solved numerically. New results are obtained concerning the value of the angle and the speed for which the longest distance and the longest duration glides happen, and then for which the steepest, the fastest and the most fuel economical climbs happen. The values obtained differ from those found in most airplane dynamics textbooks. Example of tables are produced that show how general speed changes can be effected efficiently; showing the time required for the changes, the horizontal distance traveled and the amount of fuel required. The results obtained apply to all internal combustion engine-propeller driven airplanes.